The present invention relates to a surface-treated component manufacturing method and apparatus for locally surface-treating steel bars (including hollow and solid steel bars), for example, rods of cylinder devices such as hydraulic cylinders and hydraulic shock absorbers.
A hydraulic shock absorber as a cylinder device provided in a traveling device, e.g. an automobile, substantially comprises a cylinder incorporating a piston, and a rod connected at one end thereof to the piston in the cylinder and retractably projecting at the other end thereof from the cylinder through a rod guide.
The rod has an annular stopper (rebound stopper) attached to the outer periphery of an axially intermediate portion thereof. The stopper abuts against the rod guide when the rod is extended, thereby defining the most extended position of the rod. The stopper is secured to the rod by what is called metal flow joining. That is, a full-circumferential groove is formed on the outer peripheral surface of the rod, and a part of the stopper is pushed into the full-circumferential groove through plastic deformation.
In the process of manufacturing such a rod, a steel bar (steel base material) as a blank (material) for a rod is locally quenched. That is, a steel bar is locally quenched to form quenched portions in regions other than those to be subjected to plastic working or cutting, e.g. both ends of the steel bar and a region where a full-circumferential groove is to be formed (for example, see Japanese Patent Laid-Open Publication No. 2013-209709).